How do you add detail to a Use Case Diagram using sub-diagrams?

Draw a high-level diagram first, then "explode" each complex use case into its own sub-diagram of finer-grained use cases — layering detail instead of cramming it all onto one page.

This keeps a big system readable: the top diagram is the overview anyone can grasp, and each sub-diagram zooms into one capability without drowning the reader in detail they don't need yet.

Process:

1. Create initial design with high-level use cases
2. For each complex UC, create a separate sub-diagram
3. Add new use cases that make up the top-level ones
4. Use <<include>> and <<extend>> relationships

Airline Example:

• Initial: Ticket Clerk -> [Check-In Passenger], [Add Reservation], [Cancel Reservation]
• Sub-diagram for Check-In: [Weigh Luggage], [Assign Seat], [Check Available Space], [Record Passenger Info], [Update Seating Chart]

Benefit: Manages complexity by layering detail progressively.